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Argument of complex number - Practice Questions & MCQ

Edited By admin | Updated on Sep 18, 2023 18:34 AM | #JEE Main

Quick Facts

  • 12 Questions around this concept.

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Let w1 be the point obtained by the rotation of z1 = 5 + 4i about the origin through a right angle in the
anticlockwise direction, and w2 be the point obtained by the rotation of z2 = 3 + 5i about the origin through a right angle in the clockwise direction. Then the principal argument of w1 – w2 is equal to :

Concepts Covered - 1

Argument of complex number

If a complex number z = x + iy is represented by a point P in the Argand plane and OP forms some angle with a positive x-axis, let's denote it with ?, then ? is called the argument of z.

$\begin{aligned} & \tan \theta=\frac{\mathrm{PM}}{\mathrm{OM}} \\ & \tan \theta=\frac{\mathrm{y}}{\mathrm{x}}=\frac{\operatorname{Im}(\mathrm{z})}{\operatorname{Re}(\mathrm{z})} \Rightarrow \theta=\tan ^{-1} \frac{\mathrm{y}}{\mathrm{x}} \\ & \arg (\mathrm{z})=\theta=\tan ^{-1} \frac{\mathrm{y}}{\mathrm{x}}\end{aligned}$

If ? lies between -? < ? ≤ ?, then ? is called the principal argument. The value of the argument differs depending on which quadrant point (x,y) lies.

If it lies in 1st quadrant then it is ? (acute angle)


 

 

If the point lies in 2nd quadrant, then  $\arg (z)=\theta=\pi-\tan ^{-1} \frac{y}{|x|}$ 

So it will be an obtuse +ve angle

If the point lies in lies in 3rd quadrant then  $\arg (z)=\theta=-\pi+\tan ^{-1} \frac{y}{x}$

It will be an obtuse -ve angle

 

If the point lies in 4th quadrant then  $\arg (z)=\theta=-\tan ^{-1} \frac{|y|}{x}$

It will be a -ve acute angle

Note:

If $\arg (\mathrm{z})=\frac{\pi}{2}$ or $-\frac{\pi}{2}, \mathrm{z}$ is purely imaginary.
If $\arg (\mathrm{z})=0$ or $\pi, \mathrm{z}$ is purely real.

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Argument of complex number

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